1. Field of the Invention
This invention relates to sliders for sliding clasp fasteners or zippers and has particular reference to an automatic locking slider of the type which generally comprises a slider body, a pull tab and a locking spring member.
2. Prior Art
A typical example of conventional sliders of the type described incorporates a locking spring member secured to the slider body in such a manner that a portion of the spring member can, under the control of the pull tab, move into and out of the passage of the sliding clasp fastener elements within a channel defined by and between the upper and lower shields or wings which constitute the slider body. The locking spring member is made of a resilient material, usually a stainless steel such that can provide sufficient resiliency to retain the slider in locked position against accidental displacement with respect to the fastener.
Known locking sliders however have a drawback in that when their associated fastener stringers are attached to a relatively heavy, hard article such as jeans, canvas, leather and the like, the slider is liable to get loose and forced out of its locked position under the influence of severe stresses tending to split the fastener stringers laterally apart or toss them up. This is primarily due to insufficient mechanical strength and resiliency of the locking spring member. However, the choice of stainless steel for the locking member that has sufficiently high cold rolling modulus and spring coefficient to withstand such stresses is often limited by the bending and shearing operation involved in shaping the material into a relatively small, complicated configuration. If a given strip of steel is subject to bending in a complicated manner, the strip would often become fractured during its bending.